1. Field of the Invention
The invention relates to steam turbine power plants, and in particular, to a method and apparatus for testing the movability of valve plugs used with the turbine generator.
2. Description of the Prior Art
In general, a nuclear steam turbine power plant includes a series connected arrangement having a steam generator element, a high pressure turbine element and a low pressure turbine element with a combined moisture separator reheater disposed therebetween. Interconnected within the plant are various flow control devices whose function is to modulate and/or completely interdict the flow of motive steam within the power plant.
It is well known that such flow control members are susceptible to buildup of frictional forces therewithin, which, if undetected, could cause premature failure of the valve and an attendant emergency condition within the power plant. It is for this reason that the various regulatory agencies concerned with the safety of such generating stations mandate frequent valve testing and inspections in order to ascertain their availability.
However, in the prior art, valves are tested while the system is at a reduced load level, since each valve tested must be completely closed and then reopened. These valve movements, if done at full load, would cause a significant, sudden change in load. Thus, by reducing load, and then closing and reopening each valve, the movability of each valve plug may be checked without significantly changing load.
The form of valve testing has, in the past, been generally accomplished not oftener than once per week. Recent statements from regulatory agencies charged with the review of safety practices indicate a desire to have daily valve testing provided. To meet this goal using traditional, prior art, valve testing techniques would require utilities to devote considerably more operating time at reduced power outputs. Further, this prospect is especially unattractive in nuclear stations because utilities wish to fully utilize the advantages of lower fuel costs and operate the higher capital cost nuclear units at as full a capacity as possible.